The present application claims priority to Japanese Application No. P2000-216121 filed Jul. 17, 2000, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to method of and apparatus for manufacturing various recording mediums such as a magnetic recording medium and an optical recording mediums for example.
2. Description of the Related Art
A recording density in an optical recording medium, for examples generally depends upon a diameter of a spot of laser beam A recording density becomes able to increase as the diameter of the spot of laser beam decreases. The diameter of the spot of laser beam is proportional to xcex/NA where xcex represents the wavelength of laser beam and NA represents the numerical aperture of objective lens. Accordingly, in order to increase the recording density of the optical recording medium, it is requested that NA should be increased by reducing the wavelength of laser beam.
In recent years, TeraStor Corporation has proposed a near-field optical disk in which a distance between an optical disk and an optical lens is under 200 nm as a method of increasing NA. Further, Quinta Corporation has proposed an optical hard disk in which an optical lens is mounted on a slider and a distance between the optical disk and the slider is less than 100 nm, or the like.
As the space between the optical system and the recording medium is reduced as described above, it is requested that the surface of the optical recording medium should be formed as a highly-smooth surface.
As the NA of the optical system increases, the pitch or the track width should be reduced more with respect to the tracking direction.
In the existing optical disk manufacturing methods, it is customary that very small concavities and convexities on the surface to construct recording pits or tracking guide grooves of the optical disk are formed by injection molding at the same time the substrate of the optical disk is molded Also in this case, the surface of the optical disk is treated by smoothing processing.
When the surface of the magnetic recording medium incorporated in a conventional hard disk apparatus is finished, as shown in a schematic perspective view of FIG. 1, a medium 40 is rotated at high speed in the direction shown by an arrow a with respect to the axis perpendicular to the surface treated by surface smoothing processing (this surface will hereinafter be referred to as a xe2x80x9csurface smoothing treatment surfacexe2x80x9d). On the other hand, a polishing work tape 41 is moved in the direction shown by an arrow b along the rotational direction of the medium 40 at linear velocity sufficiently lower than rotational linear velocity of the medium 40 while its polishing material surface is located in the vicinity of the surface smoothing treatment surface.
Then, a pressure roller 42 whose axis direction is located in the radial direction presses the surface smoothing treatment surface from above this polishing work tape 41.
Although this pressure roller 42 is rotated as the polishing work tape 41 is moved, its rotary axis is prevented from being moved. In this case, a pressure area 43 in which the medium 40 is pressed by the polishing work tape 41 becomes a straight area presented along the axial direction of the pressure roller 42.
This straight pressure area 43 is extended over the whole area along the radial direction of the medium 40 that should be treated by surface polishing process.
In the recording medium whose surface has been smoothed by the above method, i.e., concavities and convexities have been removed from the surface of the recording medium, the surface of the recording medium can be smoothed to an extent that its so-called glide height is made less than 100 nm e.g., about 30 nm.
However according to the above method, as FIG. 2 shows the state in which the polishing work tape 41 is pressing the medium 40, when a protrusion 44 is existing on the side of the polishing work tape 41 or when a hard foreign substance is caught in the polishing work tape 41, a scratch 45 occurs on the surface smoothing treatment surface 3 due to the protrusion 44 or the hard foreign substance.
Having studied and considered the occurrence of the scratch 45, the assignee of the present application clarified that the occurrence of the scratch 45 considerably depends upon the pressed state of the polishing work tape 41.
Specifically, as described above, when the straight pressure area 43 is formed by the pressure roller 42, the pressure area 43 is formed over a wide range in the radial direction of the medium 40. Accordingly, as shown by an arrow c in FIG. 2, since substantially uniform pushing force is given to the whole area of the pressure area 43, this pushing force is concentrated on the tip end in which the protrusion 44 protruded toward the surface smoothing treatment surface 3 or the caught foreign substance is butted against the surface smoothing treatment surface 3.
The assignee of the present application has clarified that the surface smoothing treatment surface tends to be scratched due to the above reason.
In view of the aforesaid aspect, it is an object of the present invention to provide method of and apparatus for manufacturing recording medium in which occurrence of scratches can be avoided effectively.
It is another object of the present invention to provide method of and apparatus for manufacturing recording medium in which highly-reliable recording mediums can be obtained.
According to an aspect of the present invention, there is provided a recording medium manufacturing method of providing a recording medium by treating a medium surface in a surface smoothing process. This recording medium manufacturing method is comprised of the steps of rotating the medium about an axis perpendicular to a surface which is treated by the surface smoothing process, smoothing the surface smoothing treatment surface of the medium by slidably contacting a polishing work tape with the surface smoothing treatment surface with partial pressure and selecting the partial pressure at very small area.
In particular, according to the present invention, the partial pressure area is selected to be less than 1 mm, more preferably, 0.5 mm with respect to both radial direction and tangential direction relative to rotation of the medium.
In accordance with another aspect of the present inventions there is provided a recording medium manufacturing apparatus for providing a recording medium by processing a medium surface by a surface smoothing treatment. This recording medium manufacturing apparatus is comprised of rotating means for rotating the medium about an axis perpendicular to a surface on which the surface smoothing treatment is effected, a polishing work tape and pressure means for partly pressing the polishing work tape against the surface smoothing treatment surface of the medium, wherein a partial pressure area provided by the pressure means is selected to be less than 1 mm with respect to both of radial direction and tangential direction relative to rotation of the medium.
In particular, the partial pressure area provided by the pressure means is selected to be less than 1 mm, more preferably, less than 0.5 mm with respect to both of radial direction and tangential direction relative to rotation of the medium.
As described above, since the pressure area in which the polishing work tape presses the surface of the medium is specified, occurrence of scratches can be decreased considerably.